package cn.seocoo.platform.common.utils;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.text.SimpleDateFormat;

/**
 * @ClassName: CodeGeneratorUtils
 * @description: 唯一Code生成
 * @author: wujian
 * @Date: 2019-07-04 23:23
 **/
public class CodeGeneratorUtils {


        private static long workerId;   //用ip地址最后几个字节标示
        private static long datacenterId = 0L; //可配置在properties中,启动时加载,此处默认先写成0
        private static long sequence = 0L;
        private static long workerIdBits = 8L; //节点ID长度
        //private long datacenterIdBits = 2L; //数据中心ID长度,可根据时间情况设定位数
        private static long sequenceBits = 12L; //序列号12位
        private static long workerIdShift = sequenceBits; //机器节点左移12位
        private static long datacenterIdShift = sequenceBits + workerIdBits; //数据中心节点左移17位
        private static long sequenceMask = -1L ^ (-1L << sequenceBits); //4095
        private static long lastTimestamp = -1L;

        public CodeGeneratorUtils() {
            workerId = 0x000000FF & getLastIP();
        }

        /**
         * 调用该方法，获取序列ID
         * @return
         */
        public static synchronized String nextId() {
            long timestamp = currentTime(); //获取当前毫秒数
            //如果服务器时间有问题(时钟后退) 报错。
            if (timestamp < lastTimestamp) {
                throw new RuntimeException(String.format("时钟向后移动。拒绝在%d毫秒内生成id", lastTimestamp - timestamp));
            }
            //如果上次生成时间和当前时间相同,在同一毫秒内
            if (lastTimestamp == timestamp) {
                //sequence自增，因为sequence只有12bit，所以和sequenceMask相与一下，去掉高位
                sequence = (sequence + 1) & sequenceMask;
                //判断是否溢出,也就是每毫秒内超过4095，当为4096时，与sequenceMask相与，sequence就等于0
                if (sequence == 0) {
                    timestamp = nextMillis(lastTimestamp); //自旋等待到下一毫秒
                }
            } else {
                sequence = 0L; //如果和上次生成时间不同,重置sequence，就是下一毫秒开始，sequence计数重新从0开始累加
            }
            lastTimestamp = timestamp;

            long suffix = (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;

            // 格式化日期
            SimpleDateFormat timePe = new SimpleDateFormat("yyyyMMddHHMMssSSS");
            String datePrefix = timePe.format(timestamp);

            return datePrefix + suffix;
        }

        /**
         * 比较当前时间戳和下一个时间戳，如果下一个时间戳等于或小于当前时间戳，则循环获取下个时间戳
         * 该方法主要是避免同一时间获取同一时间戳
         * @param lastTimestamp
         * @return
         */
        protected static long nextMillis(long lastTimestamp) {
            long timestamp = currentTime();
            while (timestamp <= lastTimestamp) {
                timestamp = currentTime();
            }
            return timestamp;
        }

        /**
         * 获取系统当前时间戳
         * @return
         */
        protected static long currentTime() {
            return System.currentTimeMillis();
        }

        /**
         * 获取当前本地IP
         * @return
         */
        private static byte getLastIP(){
            byte lastip = 0;
            try{
                InetAddress ip = InetAddress.getLocalHost();
                byte[] ipByte = ip.getAddress();
                lastip = ipByte[ipByte.length - 1];
            } catch (UnknownHostException e) {
                e.printStackTrace();
            }
            return lastip;
        }

    }

